1) Field of the Invention
The invention relates to a hydrorefining catalyst containing ruthenium sulphide, to its synthesis and to a process for hydrorefining hydrocarbon feedstocks using the said catalyst.
2) Background Art
Petroleum oil and the petroleum fractions obtained by distillation or treatment of petroleum oil are complex mixtures in which, besides hydrocarbons, there are compounds containing heteroatoms such as sulphur, nitrogen and oxygen. Heavy feedstocks, the use of which is becoming widespread, contain large quantities of heteroatomic compounds. These heavy feedstocks consist, for example, of heavy crudes, of bituminous schists or of heavy residues from oil refineries.
The heteroatomic compounds are impurities which are detrimental to the good quality of petroleum products. They are responsible in particular for problems linked with contamination, corrosion, odor and stability. Sulphur and nitrogen compounds can also poison the usual catalysts for the refining processes.
It is therefore important to remove them during the refining. In general this involves a hydrogen treatment in the presence of a catalyst which promotes the rupture of the carbon-heteroatom bonds. This treatment is called hydrorefining.
The main hydrorefining reactions are desulphurization and denitrification. Desulphurization consists in converting the sulphur contained in the organic compounds into hydrogen sulphide. Denitrification consists in converting the nitrogen in the organic compounds into ammonia.
Considerable research effort has been deployed to find effective hydrorefining catalysts which resist deactivation by heteroatoms.
The most commonly employed hydrorefining catalysts are based on nickel, molybdenum, tungsten or cobalt. These metals are deposited onto supports by impregnation with the aid of their water-soluble- salts and are then converted into sulphides.
The supports are generally based on refractory oxides such as alumina or silica-aluminas.
The use of zeolite supports has also been investigated.
The crystalline structure of zeolites consists of AlO.sub.4 and of SiO.sub.4 tetrahedra joined together by oxygen atoms common to two tetrahedra. The three-dimensional framework formed by the assembly of these tetrahedra has cavities and channels which accommodate the cations compensating for the charge deficit linked with the presence of trivalent ammonium in the AlO.sub.4 tetrahedra. Before the catalysts are prepared, these compensating cations are exchanged with hydrogen ions.
The catalytically active forms are obtained by introduction of metals with a catalytic effect into this acidic form.
Phillips Petroleum U.S. Pat. No. 4,324,647 describes, for example, a hydrocracking, hydrodesulphurizing and hydrodenitrifying process using a catalyst based on zeolite Y. This zeolite is employed in acidic form. Its sodium concentration is preferably below 0.2% by weight.
Patent Application PCT WO 86/01743 suggests associating a zeolite Y preferably containing 0.5 to 3% by weight of ruthenium with the conventional bimetallic hydrotreatment catalysts on alumina. Here again the zeolite is employed in acidic form.